1. Technical Field of the Invention
The present invention relates to novel 4,4-dihydroxy-5-pyrazolinones, to processes for their preparation and the formulation thereof into cosmetic/dermatological compositions well suited for coloring the skin and/or the hair, and also for coloring certain areas of the skin, in particular the face, in order to impart a healthy appearance thereto by enhancing the radiance of the complexion while at the same time retaining transparency.
This invention also relates to the use of the subject compounds in the cosmetics field for the coloration of the skin and, more particularly, for imparting a tanned appearance to the skin.
2. Description of the Prior Art
It is known to this art that dihydroxyacetone, or DHA, is a particularly advantageous compound commonly used in cosmetics as an agent for artificially tanning or browning the skin; when applied to the skin, in particular to the face, it affords a tanning or browning effect which is very similar in appearance to that which can result from prolonged exposure to the sun (a natural tan) or under a UV lamp. Such use also presents the advantage of entirely avoiding the risks of skin reaction generally associated with the aforementioned prolonged exposures (erythema, burning, loss of elasticity, appearance of wrinkles, premature aging of the skin, and the like).
However, the use of DHA has certain drawbacks.
For example, although the color produced on the skin by applying a composition containing DHA is very close to that obtained in a natural tan, certain users may still consider it to be too yellow.
Other drawbacks also appear during the storage of compositions containing DHA. Thus, DHA has an annoying tendency, which may be more or less pronounced depending on the nature of the medium in which it is formulated, to degrade over time, this degradation generally leading in the long term to an undesirable yellowing of the compositions containing same. Over time, such compositions may also develop a nauseating odor. Lastly, the pH of compositions containing DHA decreases over time, making them in the long run incompatible for topical application. These various phenomena have the effect of greatly reducing the activity of DHA, and in particular its ability to color the skin, when such compositions are topically applied onto the skin.
Moreover, the intensity of the coloration obtained on the skin, and especially the speed with which this coloration develops, are often considered to be insufficient by users of DHA-based self-tanning products, since the time required for the desired intensity to appear on the skin is generally several hours.
In order to increase the speed of appearance of the coloration due to DHA, it has been sought to combine it with other active species. Thus, EP-A-547,864 describes providing DHA in the presence of an amino acid and a silicone, the DHA and the amino acid being stored in separate compartments before they are applied to the skin. Mention may also be made of WO-A-94/04130 which describes a device for supplying DHA at the same time as a primary amine, these two compounds also being stored in separate compartments.
Nonetheless, these devices present the drawback of being complicated and of not providing any real improvement as regards the waiting time required in order to obtain a satisfactory coloration on the skin. Lastly, in addition, they do not totally solve the problems due to the storage of compositions containing DHA.
Thus, it appears that DHA as an agent for artificially coloring the skin is not completely satisfactory and serious need continues to exist for other active agents which, preferably, do not present any of the disadvantages and drawbacks above.